A year or so ago, I finally managed to upgrade my graphics hardware from the on-board to a PCX video card -- expecting, among other things, to see BOINC start using my GPU for computation.

That's never happened, I just have two work units at a time, one for each CPU core. I've recently discovered that this is because my GPU (on a video card I bought for Christmas 2012) is too old/slow (nVidia GT520, 128 MB DDR2). Despite up to date drivers and appropriate support in the drivers for GPU computing, apparently I don't have enough computing power factor in this card (even though it's many times better than the video hardware I used to have).

My question is, why the lower limit? My GPU should still be capable of several times the performance of each of my CPU cores; even with the overhead of running a Windows XP or MEPIS 11 Linux desktop, it ought to let me produce close to twice as many work units per day as the CPU alone.

Older/budget computers need not apply?

I could be wrong but the only relevant data I can find shows that it would actually take longer to process on your current GPU than your CPU.
http://www.dskag.at/images/Research/EinsteinGPUperformancelist.pdf

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IIRC your GPU does not support "double precision" which is needed here, see also the GPU Requirements Thread. You should see messages about it in your log. The card is not too old or slow, it simply can't perform the flowting point calculations with the reqired precision.

Most projects does not require that feature, SETI@Home, which you also have in your project list, will run fine on that card.

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A year or so ago, I finally managed to upgrade my graphics hardware from the on-board to a PCX video card -- expecting, among other things, to see BOINC start using my GPU for computation.

That's never happened, I just have two work units at a time, one for each CPU core. I've recently discovered that this is because my GPU (on a video card I bought for Christmas 2012) is too old/slow (nVidia GT520, 128 MB DDR2). Despite up to date drivers and appropriate support in the drivers for GPU computing, apparently I don't have enough computing power factor in this card (even though it's many times better than the video hardware I used to have).

My question is, why the lower limit? My GPU should still be capable of several times the performance of each of my CPU cores; even with the overhead of running a Windows XP or MEPIS 11 Linux desktop, it ought to let me produce close to twice as many work units per day as the CPU alone.

Older/budget computers need not apply?

Here is a link http://www.setiusa.us/content.php?119-BOINC-GPU-Compatibility-List for the different Boinc projects that can use a gpu and the specs for each. I heard that Seti is out of gpu units at the moment but that could change at anytime, if they are still out try another project of your liking. Be aware that not all have units all the time, Poem for instance is rationing units right now, and probably will be for a while, it is a hit or miss thing.

Yep, okay, that's the deal -- no double precision floating point capability (in fact, that appears to be the only significant difference between CC 1.2 and 1.3).

Essentially, then, if you want to add GPU computation, at least on MilkyWay@home, you need to spend around $120+ on each video card for PCX, or $100+ for plain PCI (mine was, as I recall, about $70 when I got it, and was still a huge step up from the on-board graphics I had previously). That's not going to happen here any time soon...

BTW, SETI@home still shows on my projects list because that's where I started @home computing, but I haven't run SETI in a while (I had it on my Linux install for a short time, but I've dropped it again, running MilkyWay exclusively now).

I heard that Seti is out of gpu units at the moment but that could change at anytime, if they are still out try another project of your liking. Be aware that not all have units all the time, Poem for instance is rationing units right now, and probably will be for a while, it is a hit or miss thing.

SETI is not out of GPU units, they just can't generate enough of them right now. It's an issue for the top crunchers, but a 520 shouldn't be idle too much. And even if it gets idle every now and than, that's still better than idle all the time like it is now. The best solution is to have one or more backup projects for each device ready to kick in if the primary projects runs out of work. That happens with every project every now and than.

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I heard that Seti is out of gpu units at the moment but that could change at anytime, if they are still out try another project of your liking. Be aware that not all have units all the time, Poem for instance is rationing units right now, and probably will be for a while, it is a hit or miss thing.

SETI is not out of GPU units, they just can't generate enough of them right now. It's an issue for the top crunchers, but a 520 shouldn't be idle too much. And even if it gets idle every now and than, that's still better than idle all the time like it is now. The best solution is to have one or more backup projects for each device ready to kick in if the primary projects runs out of work. That happens with every project every now and than.

Thanks!! I will tell my friend.

Donald with those that gpu you might want to consider a gpu project, with the preferences you set it for gpu units only and be crunching for multiple projects.